Rename user.authtoken to user.password; drop obsolete team.authtoken.

Stop overloading the password field with multiple tokens, because
this hinders us when presenting an appropriate UI for the field.
IP address is already stored in the ip_address field.

Changes behaviour for LDAP, which will now just match user.username,
which shouldn't be problematic. Drops unused column team.authtoken.
Display team.login as "ID" to avoid confusion with user.login.
No more highlighting.php
Improve user management by allowing to set password and adding links.

User passwords may now be (re)set from the user edit page, not on
a separate genpasswds page. The latter is now reserved to only
setting bulk passwords; which is now limited to only those users
with a team role, as we probably do not want to do bulk password
setting for admins or judgehosts.
Clarify documentation
Replace SQL datetime by decimal(32,9) Unix epoch timestamps.
Change time representation to Unix epoch in code.
Format times with strftime().
Add contest starttime_string column.
Consistently use time print and diff functions.
Fix SQL upgrade script typo.
Fix HTML error.
Cleanup and bugfixes for new Unix epoch timestamps.
Parse new scoreboard layout.
Fix team interface trying to request update_clarifications.php in JS.

Not the role is relevant, but the interface we're in.
Update team manual to reflect new scoreboard layout.
Use unprivileged user to compile program to make sure that it
doesn't have access to e.g. testdata files.
Add test source exhibiting problem with compile time testdata access.
Add some Changelog entries.
Fix some PHP errors:
- check that array is passed to foreach()
- typo in function call
- suppress PHP notice for undefined variable